Effects of Voltage Stabilziers on the AC and DC Breakdown Strengths of EPDM

Voltage stabilizers are widely used to improve the electrical tree resistance and breakdown strength of cross-linked polyethylene (XLPE) insulating materials. Ethylene-Propylene-Diene Monomer rubber (EPDM), as a frequently-used material for the enhanced insulation of cable accessories or medium voltage power cable insulation, has also an urgent need for higher breakdown strength. Under working temperature, XLPE is a semi-crystalline polymer while EPDM is an amorphous polymer. As regards whether voltage stabilizers have positive effects in EPDM and whether they are easy to migrate and precipitate out of the rubber which has a loose aggregation structure, little is known. In this work, the effects of four voltage stabilizers on the AC and DC breakdown strengths of EPDM were investigated, and whether the voltage stabilizers are easy to migrate out of EPDM was verified by testing the DC breakdown strength of the samples after degassed in 80 °C vacuum oven for 100 days. Among the selected aromatic voltage stabilizers, only RBBT and AOHBP are slightly effective on improving the AC breakdown strengths of EPDM, while the four voltage stabilizers can all significantly improve the DC breakdown strength, and they are all unlikely to precipitate out of the rubber despite its looser aggregation structure than XLPE, which was confirmed by the further improved DC breakdown strength after degassed for 100d. It is proposed that voltage stabilizers can be expansively used in EPDM rubber to improve its breakdown strength.